U.S. patent number 9,658,174 [Application Number 14/538,837] was granted by the patent office on 2017-05-23 for x-ray topography apparatus.
This patent grant is currently assigned to RIGAKU CORPORATION. The grantee listed for this patent is Rigaku Corporation. Invention is credited to Takeshi Fujimura, Atsunori Kiku, Keiichi Morikawa, Kazuhiko Omote, Masahiro Tsuchiya, Yoshinori Ueji.
United States Patent |
9,658,174 |
Omote , et al. |
May 23, 2017 |
X-ray topography apparatus
Abstract
Disclosed is an X-ray topography apparatus including an X-ray
source, a multilayer film mirror, a slit, a two-dimensional X-ray
detector, and a sample moving device that sequentially moves the
sample to a plurality of step positions. The X-ray source is a
minute focal spot. The multilayer film mirror forms monochromatic,
collimated, high-intensity X-rays. The direction in which the
multilayer film mirror collimates the X-rays coincides with the
width direction of the slit. The step size by which the sample is
moved is smaller than the width of the slit. The combination of the
size of the minute focal spot, the width of the slit, and the
intensity of the X-rays that exit out of the multilayer film mirror
allows the contrast of an X-ray image produced when the detector
receives X-rays for a predetermined period of 1 minute or shorter
to be high enough for observation of the X-ray image.
Inventors: |
Omote; Kazuhiko (Akiruno,
JP), Morikawa; Keiichi (Fuchu, JP), Ueji;
Yoshinori (Akishima, JP), Tsuchiya; Masahiro
(Tachikawa, JP), Fujimura; Takeshi (Akiruno,
JP), Kiku; Atsunori (Hino, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Rigaku Corporation |
Akishima-shi |
N/A |
JP |
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Assignee: |
RIGAKU CORPORATION
(Akishima-Shi, Tokyo, JP)
|
Family
ID: |
53045648 |
Appl.
No.: |
14/538,837 |
Filed: |
November 12, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150146858 A1 |
May 28, 2015 |
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Foreign Application Priority Data
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Nov 28, 2013 [JP] |
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2013-246533 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N
23/20016 (20130101); G01N 23/20008 (20130101); G01N
23/207 (20130101); G21K 1/062 (20130101); G01N
23/20 (20130101); G01N 23/20025 (20130101); G01N
2223/6462 (20130101); G01N 2223/05 (20130101); G01N
2223/045 (20130101); G01N 2223/315 (20130101); G21K
2201/064 (20130101) |
Current International
Class: |
G01N
23/20 (20060101); G21K 1/06 (20060101); G01N
23/207 (20060101) |
Field of
Search: |
;378/71-74,79,81 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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08-124983 |
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May 1996 |
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JP |
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2006-284210 |
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Oct 2006 |
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JP |
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2007-240510 |
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Sep 2007 |
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JP |
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WO 2008/052287 |
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May 2008 |
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WO |
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Other References
http:// chelron 2010. Spring 8. Or. Jp /text/bl/11 .sub.--BL19B2
.pdf, (file stamp date: Sep. 30, 2010), "beam line BL19B2 at
Spring-8, synchrotron radiation facility", 2 pages. cited by
applicant .
"Report on current status of X-ray topography research group"
(Spring-8 User's Information/vol. 13 No. 1 Jan. 2008/Research Group
Report Spring-8 Users Society//Faculty of Science, University of
Toyama, Satoshi Iida, Graduate School of Engineering, Osaka
University, Takayoshi Shimura, Japan Synchrotron Radiation Research
Institute, Industrial Application Division, Kentaro Kajiwara), 6
pages. cited by applicant.
|
Primary Examiner: Ho; Allen C.
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Claims
The invention claimed is:
1. An X-ray topography apparatus that uses X-rays for form
two-dimensional images in correspondence with an internal structure
of a sample, comprising: an X-ray source that produces X-rays with
which the sample is irradiated; a multilayer film mirror provided
in a position between the sample and the X-ray source; a slit
member provided in a position between the sample and the X-ray
source and including a slit that limits a width of the X-rays;
two-dimensional X-ray detection means for two-dimensionally
detecting X-rays having exited out of the sample; and sample moving
means for achieving stepwise movement of the sample relative to the
X-rays with which the sample is irradiated to sequentially move the
sample to a plurality of step positions, wherein: the X-ray source
produces the X-rays from a minute focal spot, the multilayer film
mirror converts the X-rays emitted from the X-ray source into
monochromatic, collimated, high-intensity X-rays, the direction in
which the multilayer film mirror collimates the X-rays coincides
with a width direction of the slit of the slit member, the step
size by which the sample moving means moves the sample is smaller
than a width of the slit, and the combination of the size of the
minute focal spot, the width of the slit, and the intensity of the
X-rays that exit out of the multilayer film mirror allows the
contrast of an X-ray image produced when the two-dimensional X-ray
detection means receives the X-rays for a predetermined period of 1
minute or shorter to be high enough for observation of the X-ray
image.
2. The X-ray topography apparatus according to claim 1, further
comprising a processor, wherein the processor is configured to:
acquire a two-dimensional cross-sectional image associated with
each of the plurality of step positions, wherein the
two-dimensional cross-sectional image is produced by irradiating
the sample with the X-rays in each of the plurality of step
positions for the predetermined period and detecting X-rays having
exited out of the sample irradiated with the X-rays with the
two-dimensional X-ray detection means, thereby acquiring a
plurality of two-dimensional cross-sectional images, form a
three-dimensional image by arranging the plurality of
two-dimensional cross-sectional images, and acquire a second
two-dimensional image by extracting data along a flat plane
different from measurement planes associated with the
three-dimensional image.
3. The X-ray topography apparatus according to claim 2, wherein the
processor is further configured to calculate dislocation density
based on the second two-dimensional image.
4. The X-ray topography apparatus according to claim 3, wherein the
minute focal spot comprises a focal spot so sized as to fall within
a circle having a diameter of 100 .mu.m, and the width of the slit
ranges from 10 to 50 .mu.m.
5. The X-ray topography apparatus according to claim 4, wherein the
multilayer film mirror comprises a parabolic form, so as to allow
X-rays incident on the sample to be diffracted in parallel to each
other.
6. The X-ray topography apparatus according to claim 5, wherein
interplanar spacing of lattice planes in the multilayer film mirror
is so differentiated from each other location-to-location that the
X-rays incident at different angles of incidence are reflected off
the entire surface of the multilayer film mirror.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an X-ray topography apparatus that
uses X-rays to form a two-dimensional image in correspondence with
a crystal defect structure present in a single crystal sample.
Description of the Related Art
There is a known conventional X-ray topography apparatus disclosed,
for example, in Patent Citation 1 (Japanese Patent Laid-Open
Publication H08-124983). Patent Citation 1 discloses that a single
and individual X-ray topographic image is captured. Patent Citation
1, however, does not disclose that a plurality of X-ray topographic
images are acquired from a single sample.
Patent Citation 2 (Japanese Patent Laid-Open Publication
2006-284210) describes that a plurality of section topographic
images (that is, two-dimensional cross-sectional images) are
acquired by using X-rays and then caused to undergo multiple
exposure. Patent Citation 2, however, provides no detailed
description about the multiple exposure. According to typical
interpretation, the multiple exposure is believed to mean exposure
of a plurality of images superimposed on a single two-dimensional
detector by using a large amount of step movement of the
sample.
Patent Citation 3 (WO2008/052287A1) discloses that an X-ray source
as small as 10 to 50 .mu.m is used to output X-rays, that the width
of the X-rays is limited with a slit, and that a sample is moved
stepwise for acquisition of a plurality of diffraction images.
Patent Citation 3, however, does not mention the intensity of the
X-rays with which the sample is irradiated. When the X-ray source
is small and the width of the X-rays is limited with a slit, the
intensity of the X-rays that reach the sample is significantly
attenuated, which means that the sample needs to undergo very long
exposure, for example, for several hours to ten hours in order to
provide a single desired X-ray image. No one has therefore
considered acquisition of a large number of X-ray images or as many
as several hundreds of X-ray images.
Non-Patent Citation 1
(http://cheiron2010.Spring8.or.Jp/text/bl/11_BL19B2.pdf, (file
stamp date: 30 Sep. 2010), "beam line BL19B2 at Spring-8,
synchrotron radiation facility") discloses that a sample is moved
stepwise with respect to synchrotron radiation for acquisition of
section topographs of the sample irradiated with the synchrotron
radiation in each step position and that the section topographs are
superimposed on each other to provide a 3D (three-dimensional)
image. Synchrotron radiation, which inherently contains
high-intensity X-rays, allows acquisition of a plurality of section
topographs in a relatively short period. The period required to
acquire a plurality of section topographic images can therefore be
greatly shortened. It is, however, impossible to use a synchrotron
radiation facility in typical corporate research or manufacturing
situations.
Non-Patent Citation 1 does not mention at all use of a
laboratory-level X-ray source. Since a laboratory-level X-ray
source outputs low-intensity X-rays, acquisition of a plurality of
section topographs within a practically acceptable period of time
by using the X-ray source is not worth consideration.
Non-Patent Citation 2 is the "Report on current status of X-ray
topography research group" (Spring-8 User's Information/Vol. 13 No.
1 Jan. 2008/Research Group Report Spring-8 Users Society//Faculty
of Science, University of Toyama, Satoshi IIDA, Graduate School of
Engineering, Osaka University, Takayoshi SHIMURA, Japan Synchrotron
Radiation Research Institute, Industrial Application Division,
Kentaro KAJIWARA). Non-Patent Citation 2 discloses that a sample is
scanned with synchrotron radiation and cross-sectional images of
several portions of the sample irradiated with the synchrotron
radiation are captured, and that the images are superimposed on
each other in a computer for estimation of a three-dimensional
distribution of in-crystal lattice distortion. Non-Patent Citation
2 does not describe at all use of a laboratory-level X-ray source,
too. Since a laboratory-level X-ray source outputs low-intensity
X-rays, acquisition of a plurality of section topographic images
within a practically acceptable period of time by using the X-ray
source is not worth consideration.
Patent Citation 4 (Japanese Patent Laid-Open Publication
2007-240510) discloses an X-ray topography apparatus in which a
zone plate or any other X-ray collection means is used to collect
X-rays and a sample is irradiated with the collected X-rays. Patent
Citation 4 does not mention technologies for outputting X-rays from
a minute focal spot, converting X-rays into monochromatic X-rays,
collimating X-rays into a collimated beam, or increasing the
intensity of X-rays. The apparatus described in Patent Citation 4
cannot therefore acquire a large number of section topographic
images in a short period.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problems with
the conventional X-ray topography apparatus described above, and an
object of the present invention is to acquire a large number of
section topographic images or as many as several hundreds of
section topographic images by using a laboratory-level X-ray source
in a practically acceptable short period, for example, one hour to
a dozen of hours.
An X-ray topography apparatus according to the present invention is
an X-ray topography apparatus that uses X-rays to form
two-dimensional images in correspondence with a crystal defect
structure present in a single crystal sample, the apparatus
including an X-ray source that produces X-rays with which the
sample is irradiated, a multilayer film mirror provided in a
position between the sample and the X-ray source, a slit member
provided in a position between the sample and the X-ray source and
including a slit that limits the width of the X-rays,
two-dimensional X-ray detection means for two-dimensionally
detecting X-rays having exited out of the sample, and sample moving
means for achieving stepwise movement of the sample and the X-rays
with which the sample are irradiated relative to each other to
sequentially move the sample to a plurality of step positions. The
X-ray source produces the X-rays from a minute focal spot. The
multilayer film mirror converts the X-rays emitted from the X-ray
source into monochromatic, collimated, high-intensity X-rays. The
direction in which the multilayer film mirror collimates the X-rays
coincides with the width direction of the slit of the slit member.
The width of the slit is sufficiently narrower than the thickness
of the sample. The step size by which the sample moving means moves
the sample is smaller than the width of the slit. The combination
of the size of the minute focal spot, the width of the slit, and
the intensity of the X-rays that exit out of the multilayer film
mirror allows the contrast of an X-ray image produced when the
two-dimensional X-ray detection means receives the X-rays for a
predetermined period of 1 minute or shorter to be high enough for
observation of the X-ray image.
The X-ray topography apparatus allows generation of a large number
of two-dimensional cross-sectional images or as many as
several-hundred images without a huge X-ray source used in a
synchrotron radiation facility but with a laboratory-level X-ray
source within a period acceptable in research and manufacturing
processes in the industries (within one hour to a dozen of hours,
for example). Subsequent observation of the large number of
two-dimensional cross-sectional images can provide knowledge of the
structure of the sample crystal.
In the configuration described above, even when the X-ray source is
a minute focal spot source or the width of the X-rays with which
the sample is irradiated is narrowed with the slit, the intensity
of the X-rays is high enough to produce an X-ray image having
sufficiently high contrast within a predetermined period of one
minute or shorter. The intensity of the X-rays described above can
be stably achieved by using the multilayer film monochromator.
The reason why the imaging period is limited to one minute or
shorter is that an imaging period of one minute or longer requires
an impractically very long period for acquisition of several
hundreds of two-dimensional cross-sectional images.
In the configuration described above, the X-ray source formed of a
minute focal spot, the monochromatic, collimated X-rays, and the
narrow slit are requirements for acquisition of high-resolution,
clear two-dimensional cross-sectional images. The multilayer film
mirror is an element for forming monochromatic, collimated,
high-intensity X-rays. Using the multilayer film mirror to increase
the intensity of the X-rays allows the X-ray source to be a minute
focal spot, and even when the X-rays emitted from the minute focal
spot are caused to pass through the narrow slit, the increased
intensity X-rays allows an X-ray image having sufficient contrast
to be produced within a practically acceptable short predetermined
period.
In general, sufficient contrast in the field of X-ray analysis
means that a signal (S0) is sufficiently greater than noise (N) in
FIG. 4. The noise (N) is typically three times greater than the
standard deviation in background. The sufficient signal (S0) is
typically at least 1.5 times greater than the noise (N), that is,
S0.gtoreq.1.5N.
FIGS. 5 and 6 show examples of the contrast of measured data. In
the examples shown in FIGS. 5 and 6, contrast high enough for
observation is achieved. In both examples, dislocation is clearly
extracted. In the images shown in FIGS. 5 and 6, dislocation is
expressed with black dots. The profile along each of the lines
shown in FIGS. 5 and 6 shows peaks corresponding to the black dots
in the image. The S/N ratio changes with peak intensity. Since the
noise level is assumed to be about 100, the S/N ratio is about 4 at
a low peak in FIG. 5. The S/N ratio is greater than 10 at a high
peak in FIG. 6. The period of the measurement made to achieve the
results shown in FIGS. 5 and 6 is 60 seconds per image.
Based on X-ray photon statistics, which shows that the S/N ratio is
improved by a factor of 1/2 power of a measurement period of time,
even when the measurement period of 60 seconds is shortened by a
factor of 1/4 to 15 seconds, an S/N ratio of 2 can be theoretically
ensured at the low peak in FIG. 5.
The multilayer film monochromator 50 is a monochromator formed by
alternately stacking a heavy element layer 51 and a light element
layer 52 multiple times on a substrate 53 having a smooth surface,
as labelled with reference character 50 in FIG. 2. The heavy
element layer 51 and the light element layer 52, each having an
appropriate thickness, are alternately and periodically stacked on
each other in an appropriate film formation method, for example, a
sputtering process. The multilayer film periodic structure provided
by repeatedly forming the stacked structure formed of the heavy
element layer 51 and the light element layer 52 periodically
multiple times allows efficient diffraction of characteristic
X-rays, for example, CuKa rays. As a result, high-intensity
diffracted X-rays R2 can be produced on the exiting side of the
multilayer film monochromator 50.
A surface P1 of the multilayer film monochromator 50 can be formed
to be parabolic. The entire parabolic surface P1 allows X-rays R1
incident thereon to be diffracted in parallel to each other.
Further, the interplanar spacing of lattice planes in the
multilayer film monochromator 50 is so differentiated from each
other location-to-location that the X-rays R1 incident at different
angles of incidence are reflected off the entire surface P1 of the
multilayer film monochromator 50. Specifically, the interplanar
spacing of lattice planes on the X-ray incident side, where the
angle of incidence is large, are small, whereas the interplanar
spacing of lattice planes on the X-ray exiting side, where the
angle of incidence is small, are large, with the interplanar
spacing of lattice planes in between the two sides continuously
changing.
As described above, when the surface P1 of the multilayer film
monochromator 50 is a parabolic surface and the interplanar spacing
of lattice planes in each position in the parabolic surface is
appropriately adjusted, the multilayer film monochromator 50
outputs the high intensity, collimated x-rays. Further, when the
total thickness of a pair of the heavy element layer 51 and the
light element layer 52, that is, a stacked thickness T2
corresponding to one cycle on the X-ray exiting side is greater
than a stacked thickness T1 on the X-ray incident side, the
intensity of the X-rays R2 outputted from the multilayer film
monochromator 50 and applied through the slit to the sample can be
higher than the intensity of the X-rays in a case where no
multilayer film monochromator 50 mirror is used.
Conceivable examples of the heavy element may include W (tungsten),
Mo (molybdenum), and Ni (nickel). Conceivable examples of the light
element may include Si (silicon), C (carbon), and B.sub.4C.
Conceivable examples of the stacked structure may include a
two-layer structure using two types of element and a multilayer
structure using at least three types of element. Further, the
number of stacked heavy element layer 51 and light element layer 52
can, for example, be about 200. Moreover, the one-cycle thickness
of the layer formed of a single heavy element layer 51 and a single
light element layer 52 can be set at a value ranging, for example,
from 20 to 120 angstroms.
In the X-ray topography apparatus according to the present
invention, irradiating the sample with the X-rays in each of the
plurality of step positions for the predetermined period and
detecting X-rays having exited out of the sample irradiated with
the X-rays with the two-dimensional X-ray detection means allow
acquisition of a two-dimensional cross-sectional image associated
with each of the step positions, formation of a three-dimensional
image by arranging the plurality of two-dimensional cross-sectional
images, and acquisition of a second two-dimensional image by
extracting data along a flat plane different from the measurement
planes associated with the three-dimensional image.
In the X-ray topography apparatus according to the present
invention, dislocation density can be calculated based on the
second two-dimensional image.
In the X-ray topography apparatus according to the present
invention, the minute focal spot can be a focal spot so sized that
it falls within a circle having a diameter of 100 .mu.m, and the
width of the slit can be set at a value ranging from 10 to 50
.mu.m.
EFFECTS OF THE INVENTION
The X-ray topography apparatus according to the present invention
allows generation of a large number of two-dimensional
cross-sectional images or as many as several hundreds of
two-dimensional cross-sectional images without a huge X-ray source
used in a synchrotron radiation facility but with a
laboratory-level X-ray source within a period acceptable in
research and manufacturing processes in the industries (within one
hour to a dozen of hours, for example). Subsequent observation of
the large number of two-dimensional cross-sectional images allows
knowledge of a crystal defect structure in the sample.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment of an X-ray topography apparatus
according to the present invention;
FIG. 2 is a cross-sectional view showing an example of a multilayer
film mirror that is a key part of the X-ray topography apparatus
shown in FIG. 1;
FIG. 3 is a flowchart showing the procedure of operation performed
by the X-ray topography apparatus in FIG. 1;
FIG. 4 is a graph showing the contrast between a dislocation image
and background in an X-ray image;
FIG. 5 shows an X-ray image and a diffracted X-ray profile
corresponding to the image in an exemplary case where good contrast
is achieved;
FIG. 6 shows an X-ray image and a diffracted X-ray profile
corresponding to the image in another exemplary case where good
contrast is achieved;
FIG. 7 shows an example of two-dimensional cross-sectional images
(that is, section topographic images) produced by the X-ray
topography apparatus in FIG. 1;
FIG. 8 shows an example of a three-dimensional image produced by
the X-ray topography apparatus in FIG. 1;
FIG. 9 shows an example of a second two-dimensional image produced
by the X-ray topography apparatus in FIG. 1 (left hand side) and
conventional transmission topography image (right hand side);
FIG. 10 shows a second two-dimensional image of a plane in the
vicinity of the surface of an epitaxial film provided in an
experiment;
FIG. 11 shows a second two-dimensional image of a plane at a
location in the interface between the epitaxial film and a
substrate provided in an experiment;
FIG. 12 shows a second two-dimensional image of a plane at another
location in the interface between the epitaxial film and the
substrate provided in an experiment;
FIG. 13 shows a second two-dimensional image of a plane at a
location in the substrate provided in an experiment;
FIG. 14 shows a second two-dimensional image of a plane at another
location in the substrate provided in an experiment; and
FIG. 15 shows a second two-dimensional image of a plane on the rear
side of the substrate provided in an experiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An X-ray topography apparatus according to the present invention
will be described below based on an embodiment. The present
invention is not, of course, limited to the embodiment. In the
drawings accompanying the present specifications, each component is
drawn in some cases in a ratio different from an actual ratio for
ease of illustration of a characteristic portion of the
component.
FIG. 1 shows an embodiment of the X-ray topography apparatus 1
according to the present invention. An X-ray topography apparatus 1
shown in FIG. 1 includes a measurement system 2 and a control
system 3. The measurement system 2 includes an incident optical
system 4, a sample stage 5, and a reception optical system 6.
(Incident Optical System)
The incident optical system 4 includes an X-ray tube 11, a
multilayer film mirror 12, and a slit member 13. The X-ray tube 11
has a filament 14, which is a cathode, and a target 15, which is an
anode. When the filament 14 is energized (that is, when current is
caused to flow through filament 14), electrons are discharged from
the filament 14. An area of the surf ace of the target 15 on which
the discharged electrons are incident is an X-ray focal spot F.
Xrays are radiated from the X-ray focal spot F. The X-ray focal
spot F functions as an X-ray source. The radiated X-rays are
extracted as point-focused X-rays through an X-ray window 16. The
X-ray focal spot F of the thus extracted X-rays is a minute focal
spot having a size that falls within a circle having a diameter of
100 .mu.m. A distance D1 from the X-ray focal spot F to a sample S
is 800 mm.
The multilayer film mirror 12 is formed of the multilayer film
monochromator 50 shown in FIG. 2. The multilayer film mirror 12
converts the X-rays emitted from the X-ray tube 11 into
monochromatic, collimated, higher-intensity X-rays. The collimation
is performed in the direction along a width direction H of a slit
13a of the slit member 13. The monochromatic, collimated,
higher-intensity X-rays produced by the multilayer film mirror 12
allow generation of a large number of segment topographic images
(that is, partial two-dimensional cross-sectional images) or as
many as 400 images within a short period, as will be described
later.
The width of the slit 13a is a predetermined width ranging, for
example, from 10 to 50 .mu.m. A width of the slit 13a smaller than
10 .mu.m attenuates the intensity of the X-rays so much that clear
segment topographic images may not be produced. On the other hand,
a width of the slit 13a greater than 50 .mu.m may not produce sharp
(that is, clear) segment topographic images.
(Sample Stage)
The sample crystal (hereinafter also simply referred to as sample)
S, which is an object under measurement, is placed on the sample
stage 5. The sample stage 5 is not drawn in accordance with an
actual shape but is diagrammatically drawn. The thickness d1 of the
sample S ranges, for example, from 0.2 to 2 mm. The sample S
extends in the direction passing through the plane of view of FIG.
1. Each of a plurality of crystal lattice planes k present in the
sample S extends roughly along the direction of the thickness d1 of
the sample S. Further, the crystal lattice planes k are arranged at
equal intervals in parallel to each other along a direction roughly
perpendicular to the direction of the thickness d1 of the sample
S.
The sample stage 5 is provided with a sample moving device 20. The
sample moving device 20 can linearly move the sample stage 5
intermittently or stepwise in the direction indicated by the arrow
A. The sample moving device 20 can further linearly move the sample
stage 5 in a returning direction indicated by the arrow A'. The
directions A-A' are parallel to the surface of the sample S. The
sample moving device 20 is formed of an arbitrary linearly driving
mechanism. The linearly driving mechanism can be formed, for
example, of a mechanism using a feed screw shaft driven by a pulse
motor or any other power source. A pulse motor is a motor capable
of controlling the angle of rotation of an output shaft
thereof.
X-rays R3-1 having passed through the slit 13a of the slit member
13 penetrates the sample S in the width direction (direction of the
thickness d1 of the sample S) thereof. When the sample stage 5
moves in the direction A by a predetermined step width and the
sample S moves in the direction A by the same step width
accordingly, X-rays R3-2 are incident on the next step position on
the sample S. Thereafter, whenever the sample S moves by the fixed
step width, subsequent X-rays are incident on the respective step
positions on the sample S.
A step width Sd of the step movement (that is, intermittent
movement) of the sample S is smaller than the width of the slit 13a
of the slit member 13. As a result, among a plurality of section
topographic images (that is, two-dimensional cross-sectional
images) formed by the X-rays R3-1, X-rays R3-2, etc., adjacent
section topographic images are not separated with a gap
therebetween but can be seamlessly connected to each other.
(Reception Optical System)
The reception optical system 6 includes a two-dimensional X-ray
detector 21. The two-dimensional X-ray detector 21 extends in the
direction passing through the plane of view of FIG. 1 and receives
the X-rays having exited out of the sample S, that is, diffracted
X-rays R4 in a planar manner, that is, in a two-dimensional manner.
The two-dimensional X-ray detector 21 can, for example, be formed
of a photon-counting-type pixel two-dimensional X-ray detector
(that is, pulse-counting-type pixel array two-dimensional detector)
or a two-dimensional CCD and/or CMOS detector.
The photon-counting-type pixel two-dimensional X-ray detector is an
X-ray detector having a plurality of two-dimensionally arranged
pixels each of which directly converts a photon into an electric
signal. The two-dimensional detector is an X-ray detector having a
plurality of charge coupled device (CCD) elements arranged in a
planar manner.
(Control System)
The control system 3 is formed of a computer in the present
embodiment. Specifically, the control system 3 includes a CPU 24, a
read only memory (ROM) 25, a random access memory (RAM) 26, a
memory 27, and a bus 28, which connects the components described
above to each other. The memory 27 is formed, for example, of a
hard disk drive or any other mechanical memory or a semiconductor
memory. A printer 29, which is an example of image display means,
and a display 30, which is another example of the image display
means, are connected to the bus 28.
The X-ray tube 11, the two-dimensional X-ray detector 21, and the
sample moving device 20, which are components of the measurement
system 2, are connected to the bus 28 via an interface 31. In the
memory 27 are installed topography achieving software 34, which is
function achieving means for driving the measurement system 2 to
achieve desired topographic measurement, and dislocation density
analysis software 35, which is software for analyzing measured
data. Further, in the memory 27 is provided a data file 36, which
is an area where measured data and analyzed data are stored.
(Operation)
The operation of the X-ray topography apparatus 1 shown in FIG. 1
will next be described with reference to the flowchart shown in
FIG. 3. First, in step S1, initial adjustment is made to locate
each element in FIG. 1 in a predetermined initial position.
Measurement is then initiated in a case where an operator has
instructed initiation of the measurement (YES in step S2).
Specifically, in step S3, the X-ray tube 11 in FIG. 1 is operated
to radiate X-rays. The radiated X-rays are converted by the
multilayer film mirror 12 into monochromatic, collimated,
higher-intensity X-rays. The X-rays having undergone the processes
carried out by the multilayer film mirror 12 are then narrowed in
terms of width by the slit 13a of the slit member 13 and incident
on the sample S. Reference character R3-1 denotes the incident
X-rays in FIG. 1. The X-ray irradiation continues for a
predetermined period, for example, one minute or shorter. At this
point, when a diffraction condition is satisfied between the
incident X-rays R3-1 and the crystal lattice planes k, the
diffracted X-rays R4 are produced. The X-rays R4 are detected with
the two-dimensional X-ray detector 21 (step S4).
FIG. 7 shows an example of two-dimensional cross-sectional images
(what is called section topographic images) detected with the
two-dimensional X-ray detector 21 in FIG. 1. In FIG. 7, an
elongated rectangular image labelled with reference character G1
represents a two-dimensional cross-sectional images produced by the
incident X-rays R3-1 in FIG. 1. When a lattice defect D is present
in a path along which the incident X-rays R3-1 travels in FIG. 1,
high-intensity diffracted X-rays R4-1 corresponding to the defect
are produced in the portion where the defect is present, and the
high-intensity diffracted X-rays produce a black dot in the
two-dimensional cross-sectional image G1. That is, it is shown that
a lattice defect is present in a position in the sample S that
corresponds to the position where the black dot is formed in the
two-dimensional cross-sectional image G1.
In FIG. 7, the direction indicated by the arrows B corresponds to
the direction in which the X-rays R3-1 in FIG. 1 travel (that is,
thickness direction of sample S). The width L1 of the
two-dimensional cross-sectional image G1 in FIG. 7 corresponds to
the path along which the incident X-rays R3-1 pass through the
sample S in FIG. 1. The direction indicated by the arrow C in FIG.
7 corresponds to the scan direction C in FIG. 1. The direction
labelled with reference character E in FIG. 7 is the direction
passing through the plane of view of FIG. 1 (that is, direction
perpendicular to scan direction C along which sample S is
scanned).
The predetermined period described above for which the sample S is
irradiated with the incident X-rays R3-1 is a period that allows
sufficient contrast, that is, a sufficient S/N ratio between the
background and the black dots in the two-dimensional
cross-sectional image G1 produced by the two-dimensional X-ray
detector 21. In the present embodiment, since the multilayer film
mirror 12 is provided in the X-ray optical path in the incident
optical system 4 to increase the intensity of the X-rays, the X-ray
irradiation period can be significantly shortened as compared with
a conventional apparatus using no multilayer film mirror.
Specifically, it takes several tens of minutes for a conventional
X-ray topography apparatus to produce the single two-dimensional
cross-sectional image G1, whereas in the present embodiment, the
characteristics of the X-ray source 11 and the multilayer film
mirror 12 are so optimized that sufficient contrast is achieved in
a predetermined period of one minute or shorter, preferably 10 to
20 seconds, more preferably 10 seconds.
After the predetermined period for X-ray exposure has elapsed as
described above (YES in step S5 in FIG. 3), the CPU 24 (FIG. 1)
extracts an X-ray intensity signal from the two-dimensional X-ray
detector 21 (step S6 in FIG. 3), data carried by the signal (that
is, data corresponding to two-dimensional cross-sectional image G1
in FIG. 7) is stored in the data file 36 in the memory 27 (step S7
in FIG. 3).
When imaging using the incident X-rays R3-1 in a single position on
the sample S is completed, the CPU 24 instructs the sample moving
device 20 to move the sample stage 5 and hence the sample S by the
predetermined step width Sd in the direction indicated by the arrow
A and stop the sample stage 5 and hence the sample S in the
post-movement position (NO in step S8, step 9 in FIG. 3). The step
width Sd is, for example, 10 .mu.m. The step width Sd is set to a
value smaller than the width of the slit 13a of the slit member
13.
As a result, a state in which the incident X-rays R3-2 are incident
on an adjacent step position separated by the step width Sd is
achieved. In this state, steps S3 to S7 in FIG. 3 are repeated, and
a two-dimensional cross-sectional image G2 in FIG. 7 is produced in
the form of data in the X-ray intensity signal and stored. When a
lattice defect D is present in the path along which the incident
X-rays R3-2 travel, high-intensity diffracted X-rays R4-2
corresponding to the defect are produced, and the diffracted X-rays
produce a black dot in the two-dimensional cross-sectional image
G2.
Thereafter, the step movement of the sample S and the X-ray
measurement are repeatedly performed until a predetermined large
number of two-dimensional cross-sectional images G1, G2, . . . Gn,
for example, 400 two-dimensional cross-sectional images are
produced (NO in step S8, step S9 in FIG. 3). As a result, a large
number of two-dimensional cross-sectional images G1, G2, . . . Gn
associated with the step positions on the sample S are stored, as
shown in FIG. 7.
After the measurement is made for the predetermined number of
images (YES in step S8), and when an operator instructs analysis
(YES in step S10), the CPU 24 produces, in step S11 in FIG. 3, a
three-dimensional image J diagrammatically shown in FIG. 8 and
stores the three-dimensional image J in the memory. The
three-dimensional image J is formed by arranging the large number
of (400 in the present embodiment) two-dimensional cross-sectional
images G1, G2, G3, . . . Gn associated with the respective step
positions on the sample S in such a way that the images are
superimposed on each other in a three-dimensional coordinate system
Z. The three-dimensional coordinate system Z has a horizontal axis
representing a movement distance X, a vertical axis representing a
direction E perpendicular to the sample scan direction, and a
height axis representing the direction in which the X-rays travel
(or direction of sample thickness d1).
The CPU 24 then produces a second two-dimensional image in step S12
and stores them in the memory. Specifically, the three-dimensional
image J is sectioned along a flat plane different from the plane
where the measurement was made, and data on dislocation images
(i.e., black dots) in the flat plane are gathered and stored in the
memory. For example, in FIG. 8, data that belong to a surface P2 of
the three-dimensional image J are gathered and stored, and data
that belong to a flat plane P3 separated from the surface by a
distance d2 are gathered and stored.
The resulting second two-dimensional image is displayed, for
example, in the form of the left photograph in FIG. 9. The
photograph is a displayed image formed by measuring an SiC wafer as
the sample S in FIG. 1 to produce a three-dimensional image J, such
as that shown in FIG. 8, and gathering dislocation data in the
surface P2 or a surface in the vicinity thereof. The measurement
conditions were as follows:
Step movement intervals: 10 .mu.m
The number of acquired two-dimensional cross-sectional images
(section topographic images): 400
Measurement period spent to acquire single two-dimensional
cross-sectional image: 50 seconds
Field of view: 4 mm.times.6 mm
In the photograph, the long lines show that dislocation extends in
the flat plane, and the dots show that the dislocation extends in
the thickness direction of the sample.
The right photograph in FIG. 9 is presented for comparison purposes
and is a two-dimensional image produced by measuring the same place
of the sample using a traverse transmission topography technique,
which is a conventional topography measurement technique. In the
traverse topography technique, in which data in cross sections are
integrated in a two-dimensional X-ray detector, all dislocation
sites present in the sample are superimposed on each other, and the
operator views the superimposed image. Dislocation information at a
certain depth in the sample cannot therefore be accurately
reflected in the image. In contrast, in the present embodiment a
result of which is shown in the left portion of FIG. 9, dislocation
information in the flat plane at the certain depth is accurately
reflected. It is therefore clearly shown that the present
embodiment allows accurate discrimination between and
identification of basal plane dislocation, threading screw
dislocation, and threading edge dislocation.
The CPU next calculates dislocation density in step S13 in FIG. 3.
That is, dislocation density (number of dislocation sites/cm.sup.2)
is calculated based on dislocation images in the flat plane that
are produced in the form of the left photograph in FIG. 9.
Thereafter, image display using the display 30 is performed as
required (steps S14, S15), and image printing using the printer 29
is further performed as required (steps S16, S17).
As described above, the present embodiment allows measurement of a
high-contrast image of dislocation present in a cross section along
an incident X-ray beam. A large number of X-ray measurement are
made while a cross section irradiated with X-rays is slightly
shifted whenever single X-ray measurement is made for acquisition
of a large number of section topographic images, and analysis of
the section topographic images provides a three-dimensional
structure of dislocation in a wafer. Cutting the resultant
three-dimensional image in a direction parallel to the surface of
the sample provides an image of dislocation present in a plane at a
fixed depth.
The present embodiment allows observation of dislocation present in
a position in the vicinity of a surface and observation of only
dislocation present at a fixed depth from the surface. Comparison
of the present embodiment with reflective X-ray topography
measurement using synchrotron radiation has proved that threading
edge dislocation is observable.
Further, the present embodiment can provide clear knowledge of the
path along which dislocation extends. For example, it can be
determined whether dislocation is parallel to a surface, extends
from rear to front, or extend from front to rear and is redirected
back toward the front.
It can further be evaluated that the surface of a sample has many
dots representing threading dislocation or the interior of the
sample has may lines representing basal plane dislocation.
Other Embodiments
The present invention has been described with reference the
preferable embodiment, but the invention is not limited thereto and
a variety of changes can be made thereto within the scope of the
invention set forth in the claims.
For example, the multilayer film mirror 12 in FIG. 1 is not limited
to a multilayer film mirror shaped as shown in FIG. 2 and can be
arbitrarily shaped as required. Further, the control procedure
shown in FIG. 3 is an example and can be modified as required.
EXAMPLES
A crystal formed by growing an SiC epitaxial film on an SiC
substrate to a thickness of about 10 .mu.m, that is, a
homoepitaxial crystal, which is grown under the condition that the
substrate and the film are made of the same crystal, was measured
as a sample by using the X-ray topography apparatus in FIG. 1. As a
result, a second two-dimensional image of a plane in the vicinity
of the surface of the epitaxial film was produced as shown in FIG.
10. Further, a second two-dimensional image of a plane at an
interface between the epitaxial film and the substrate was produced
as shown in FIG. 11. Moreover, a second two-dimensional image of a
plane at another interface between the epitaxial film and the
substrate was produced as shown in FIG. 12. Further, a second
two-dimensional image of a plane at a location in the substrate was
produced as shown in FIG. 13. Moreover, a second two-dimensional
image of a plane at another location in the substrate was produced
as shown in FIG. 14. Further, a second two-dimensional image of a
plane on rear side of the substrate was produced as shown in FIG.
15.
EXPLANATION OF SYMBOLS
1. X-ray topography apparatus, 2. Measurement system, 3. Control
system, 4. Incident optical system, 5. Sample stage, 6. Reception
optical system, 11. X-ray tube, 12. Multilayer film mirror, 13.
Slit member, 13a. Slit, 14. Filament (cathode), 15. Target (anode),
16. X-ray window, 20. Sample moving device, 21. Two-dimensional
X-ray detector, 27. Memory, 28. Bus, 29. Printer (image display
means), 30. Display (image display means), 31. Interface, 34.
Topography achieving software, 35. Dislocation density analysis
software, 36. Data file, 50. Multilayer film monochromator, 51.
Heavy element layer, 52. Light element layer, 53. Substrate, B.
Direction along thickness of sample, C. Direction in which sample
is scanned by X-rays, D. Lattice defect, D1. Distance from X-ray
focal spot to sample, d1. Thickness of sample, d2. Separated planes
distance, E. Direction perpendicular to scanning direction, F.
X-ray focal spot (X-ray source), G1, G2, G3, . . . Gn.
Two-dimensional cross-sectional image, H. Direction of slit width,
J. Three-dimensional image, k. Crystal lattice planes, L1. Width of
two-dimensional cross-sectional images, P1. Surface, P2,P3. Planes
for sectioning three-dimensional image, R1: Incident X-rays, R2:
Diffracted X-rays, R3-1,R3-2: Incident X-rays, R4-1,R4-2:
Diffracted X-rays, S: Sample crystal, Sd: Step width, T1: Stacked
layer thickness on X-ray incident side, T2: Stacked layer thickness
on X-ray exiting side, X: Horizontal axis representing sample
moving distance, Z: Three-dimensional coordinate system,
* * * * *
References